The present invention relates to the field of information storage and retrieval using integrated circuit technology. More specifically, the present invention relates to techniques for storing and retrieving analog or digital data, or both, within an integrated circuit using multilevel nonvolatile cells.
In the real world, information comes in both digital and analog forms. Some examples of analog information include voices, sounds, images, video and electromagnetic radiation. Digital data includes binary information used in computers and electronic systems. There are digital integrated circuit memories such as DRAMs, SRAMs, Flash, and EEPROM memories. There are also analog integrated circuit memories. Some examples of analog integrated circuit memories are described in U.S. Pat. Nos. 5,694,356, 5,680,341, 5,745,409, 5,748,534, 5,748,533, 5,818,757, and U.S. provisional patent application Nos. 60/091,326 and 60/116,760, all incorporated by reference.
Although these types of memory devices have met with substantial success, there is a need for devices that will store both analog and digital information. As an example, in telephony applications, it is desirable to have an answering machine memory chip that can store both voice messages and digital information such as phone numbers. These memory devices should store the analog or digital data directly, without requiring the additional processing time and complexity of, for example, translating analog information into a digital form. Techniques are also needed for an analog and digital memory that will facilitate further miniaturization in electronics for use in such devices as voice recorders, cellular phones, animal- or human-implantable devices, and others.
Therefore, techniques and devices are needed for storing and retrieving analog and digital data using integrated circuit technology.